1. Field of the Invention
The present invention relates to improvements to methods and apparatus as described in French Pat. No. 71.40737, published under No. 2,161,129 (U.S. Pat. No. 3,789,834).
One of the main advantages of the invention described in this patent is that it permits accurate measurement of the variations in time in the electrical resistivity, or in values associated with this resistivity, relating to a defined volume of the body which is acted on by an electromagnetic field of a predetermined frequency.
2. Description of the Prior Art
It frequently happens that physiological phenomena under examination are influenced by other phenomena, even in a well defined area, such that it may be important to determine the simultaneous variations in the resistivities of more limited partial volumes constituting the area to be examined.
There are numerous methods for obtaining internal images of the body, for example, X-ray examination, scintigraphy based on injection of radioactive tracers, ultrasonic echography, thermography, but all of these methods are only effective in specific areas and none of these methods is individually capable of apprehending all of the phenomena under examination.